SWODY1
SPC AC 270600
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT WED AUG 27 2008
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MIDDLE MISSOURI
VALLEY/CORN BELT...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF NC/VA/WV...
...SYNOPSIS...
AMPLIFIED LARGE SCALE PATTERN WILL PERSIST OVER THE NORTHERN TIER OF
STATES/SOUTHERN CANADA THROUGH THE PERIOD. INITIAL POTENT SHORTWAVE
TROUGH OVER THE NORTHERN PLAINS WILL QUICKLY ADVANCE
NORTH-NORTHEASTWARD OVER THE CENTRAL CANADIAN PROVINCES...WHILE A
SECONDARY SHORTWAVE TROUGH REINFORCES THE LONGWAVE TROUGH OVER THE
NORTHERN INTERMOUNTAIN REGION/NORTHERN PLAINS. FARTHER EAST...UPPER
RIDGE WILL PERSIST OVER THE NORTHEAST STATES/EASTERN CANADA...WITH
REMNANTS OF TROPICAL DEPRESSION FAY GRADUALLY WEAKENING/SPREADING
NORTH-NORTHEASTWARD OVER THE OHIO VALLEY AND CENTRAL/SOUTHERN
APPALACHIANS.
...UPPER MIDWEST/MIDDLE MISSOURI VALLEY/CENTRAL PLAINS...
AS THE LONGWAVE TROUGH GRADUALLY SHIFTS EASTWARD OVER THE NORTHERN
PLAINS/UPPER MIDWEST TODAY...SYNOPTIC COLD FRONT WILL CONTINUE TO
MIGRATE EAST-SOUTHEASTWARD ACROSS MN/EASTERN SD AND NEB. WITH
ONGOING SHOWERS/TSTMS EXPECTED TO WANE IN MOST AREAS DURING THE
MORNING...ADDITIONAL TSTM DEVELOPMENT/INTENSIFICATION SEEMS LIKELY
LATER THIS AFTERNOON/EARLY EVENING. ALONG WITH A MOIST/UNSTABLE
PREFRONTAL AIRMASS...THIS DEVELOPMENT WILL BE FURTHER AIDED BY THE
LATE AFTERNOON/EVENING ARRIVAL OF LARGE SCALE ASCENT ASSOCIATED WITH
A SECONDARY SHORTWAVE TROUGH/MID LEVEL JET MAX. THIS SECONDARY BOUT
OF LARGE SCALE FORCING MAY CAUSE THE COLD FRONT TO RETREAT
NORTHWESTWARD DURING THE AFTERNOON/EVENING. AHEAD OF THE
FRONT...MLCAPE WILL LIKELY RANGE FROM 250-1000 J/KG ACROSS MN...TO
2000-2500 J/KG ACROSS PORTIONS OF CENTRAL/EASTERN NEB AND NORTHERN
KS. ALTHOUGH THE STRONGEST FLOW ALOFT WILL GENERALLY LAG BEHIND THE
COLD FRONT...AS MUCH AS 35-40 KT OF EFFECTIVE BULK SHEAR COINCIDENT
WITH THE FRONTAL ZONE WILL SUPPORT SOME SUPERCELLS ALONG WITH
WELL-ORGANIZED MULTICELLS. OVERALL...SEVERE HAIL/WIND WILL BE THE
PRIMARY THREAT THROUGH THE AFTERNOON/EVENING HOURS...ALTHOUGH A
TORNADO RISK CANNOT BE RULED OUT WITH INITIAL LATE AFTERNOON/EARLY
EVENING DEVELOPMENT.
...CAROLINAS/VA/WV INTO THE UPPER OHIO VALLEY...
REMNANTS OF DEPRESSION FAY WILL CONTINUE TO WEAKEN/BECOME MORE
EXTRATROPICAL IN NATURE TODAY. ON THE EASTERN PERIPHERY OF RESIDUAL
FAY...THE STRONGEST LOW LEVEL FLOW FIELDS ARE EXPECTED TO SPREAD
NORTHWARD ACROSS THE CENTRAL APPALACHIANS/UPPER OHIO VALLEY...WHERE
INSTABILITY WILL BE RATHER LIMITED ESPECIALLY WITH NORTH EXTENT.
WHILE THE OVERALL TORNADO THREAT OVER THE REGION IS EXPECTED TO BE
LESSER THAN PREVIOUS DAYS...A BRIEF/ISOLATED TORNADO RISK MAY BE
MAXIMIZED DURING THE DAYLIGHT HOURS ALONG A SLOW NORTH-LIFTING WARM
FRONT ACROSS NC INTO SOUTHERN PORTIONS OF VA/WV. WITHIN THIS
CORRIDOR...EASTERLY LOW LEVEL WINDS WILL CONTRIBUTE TO MODERATE LOW
LEVEL SHEAR/SRH...IN JUXTAPOSITION WITH A VERY MOIST AIRMASS /LOWER
70S F DEWPOINTS/ AND WEAK INSTABILITY. OTHERWISE...TSTM INDUCED WIND
DAMAGE AND/OR A ROGUE TORNADO CANNOT BE RULED ELSEWHERE ACROSS THE
CAROLINAS/FAR EASTERN GA GIVEN POTENTIAL FOR MODERATE INSTABILITY.
...AZ/LOWER CO RIVER VALLEY...
UPPER RIDGE IS FORECAST TO BUILD SOUTHEASTWARD OVER THE SOUTHWEST
DESERTS/FOUR CORNERS REGION TODAY. WHILE THERE WAS A RELATIVE LULL
IN DEEP CONVECTION ON TUESDAY...AMPLE HEATING/RECOVERY OF MID LEVEL
LAPSE RATES SHOULD RESULT IN AN UPSWING IN CONVECTIVE VIGOR WITH
ISOLATED TO PERHAPS SCATTERED TSTM DEVELOPMENT ACROSS AZ DURING THE
AFTERNOON. INCREASINGLY STRONG MID LEVEL NORTHWESTERLY FLOW /20-30
KT AT 500 MB/ WILL HELP TSTMS PROPAGATE SOUTHWESTWARD OFF THE HIGHER
TERRAIN INTO A MOIST/MODERATELY UNSTABLE AIRMASS ACROSS
SOUTHERN/WESTERN AZ.
..GUYER/BRIGHT.. 08/27/2008
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